LONDON All eyes turn to London on Friday for the opening ceremony of the 2012 Olympics, an exuberant journey from Britain's idyllic pastures through the grime of the Industrial Revolution and ending in a contemporary world dominated by popular culture.

The three-hour showcase created by Oscar-winning "Slumdog Millionaire" director Danny Boyle will be watched by a crowd of 60,000 in the main stadium built in a run-down area of London's East End and a global audience of more than a billion.

Spectators will be urged to join in sing-a-longs and help create spectacular visual scenes at an event that sets the tone for the sporting extravaganza, when 16,000 athletes from 204 countries share the thrill of victory and despair of defeat with 11 million visitors.

The Games will also answer the question on Britons' lips -- were seven years of planning, construction and disruptions, and a price tag of $14 billion during one of the country's worst recessions, actually worth it?

"This is a very, very tense moment but so far I'm cautiously optimistic," said Boris Johnson, mayor of London, the only city to host the Summer Games three times.

"I'm just worried that I haven't got enough to worry about at the moment," added the mayor, known for his witty asides.

There have, however, been bumps along the way.

Media coverage in the last few weeks has been dominated by security firm G4S's admission that it could not provide enough guards for Olympic venues, meaning thousands of extra soldiers had to be deployed at the last minute, despite its multi-million-dollar contract from the government.

Counter-terrorism chiefs have played down fears of a major attack on the Games, and British Prime Minister David Cameron said that a safe and secure Olympics was his priority.

"This is the biggest security operation in our peacetime history, bar none, and we are leaving nothing to chance."

Suicide attacks on London in July, 2005, killed 52 people, and this year also coincides with the 40th anniversary of the 1972 Munich massacre when 11 Israeli Olympic team members were killed by Palestinian militants.

Calls for an official commemoration of the tragedy at the opening ceremony have so far been refused.

Heavy traffic in central London and severe delays on Britain's creaking train system have added to the grumbling.

A diplomatic faux pas on Wednesday, when the flag of South Korea appeared at a women's soccer match between North Korea and Colombia, prompted North Korea's players to walk off the pitch and delayed kick-off by more than an hour.

"Of course the people are angry," North Korea's Olympic representative Ung Chang told Reuters. "If your athlete got a gold medal and put the flag probably of some other country, what happens?"

A series of doping scandals have also tarnished the Games' image in the buildup, with at least 11 athletes banned so far, and Greek triple jumper Paraskevi Papachristou became the Olympics' first "twitter victim" when she was withdrawn from the team over tweeted comments deemed racist.

SATANIC MILLS

All of that is likely to be forgotten as attention around the globe turns to the opening ceremony, which begins at 2000 GMT and ends more than three hours later.

While Boyle has urged the 10,000 participating volunteers and large crowds at rehearsals this week to keep the show a secret, some elements are already in the public domain.

Inspired by William Shakespeare's "The Tempest", it opens with a recreation of bucolic bliss, complete with fields, fences, hedges, sheep, geese, a shire horse, shepherdesses and even a game of village cricket.

The mood then darkens as "England's green and pleasant land", from a poem by William Blake, makes way for the sooty chimneys and smoking steel works of the "dark Satanic Mills", evoking the 19th century urban settings of Dickens.

Stirring music from Britain's past and present provides the soundtrack, which comes to the fore in the final phase, a psychedelic celebration of pop culture including songs, sitcoms and cinema classics.

Boyle's ode to the National Health Service, a politically charged topic in Britain where people are emotionally tied to the ideal of a welfare state, may make less sense to people watching from afar.

But a closing performance by ex-Beatle Paul McCartney should have global appeal for a ceremony likely to contrast sharply with Beijing's tightly choreographed, large-scale version.

Boyle had 27 million pounds ($42 million) to spend on his spectacular, well under half the amount estimated to have been spent in China in 2008.

There are still plenty of secrets, including who will have the honor of lighting the Olympic cauldron, although soccer player David Beckham and popular royal Prince William have been reported as possible torch bearers.

William's grandmother Queen Elizabeth will be in the crowd, along with U.S. First Lady Michelle Obama and a host of dignitaries and celebrities.

BOLT OR BLAKE?

The first main day of sport is Saturday, when Briton Mark Cavendish is favorite to win gold in the road race in what would be the perfect start for the home nation.

Britain's hopes are high overall after a successful Games in Beijing, although the United States, China and Russia could dominate the medals table yet again.

Among the most mouthwatering contests is the men's 100 meters final, traditionally the blue riband event of the Games, with Jamaican Usain Bolt's domination of the discipline under threat from training partner and compatriot Yohan Blake.

Bolt, fastest man on earth, is vying to do what no man has done before -- successfully defend the 100m and 200m Olympic titles, and, despite fitness concerns, he is talking tough.

"This is my time," he declared in a newspaper interview this week. "This will be the moment, and this will be the year, when I set myself apart from other athletes around the world."

If Bolt and Blake make the final, the August 5 race will rival the Carl Lewis-Ben Johnson clash at the 1988 Seoul Olympics for drama and excitement.

U.S. swimmer Michael Phelps will also be looking to cement his place as the world's greatest swimmer by adding to the eight gold medals he won in Beijing.

MANCHESTER IBF world heavyweight champion Anthony Joshua said patience would be the key to preserving his perfect knockout run after weighing in almost a stone heavier than American challenger Eric Molina on Friday.

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